/*-------------------------------------------------------------------------
 *
 * pg_shmem.h
 *      Platform-independent API for shared memory support.
 *
 * Every port is expected to support shared memory with approximately
 * SysV-ish semantics; in particular, a memory block is not anonymous
 * but has an ID, and we must be able to tell whether there are any
 * remaining processes attached to a block of a specified ID.
 *
 * To simplify life for the SysV implementation, the ID is assumed to
 * consist of two unsigned long values (these are key and ID in SysV
 * terms).  Other platforms may ignore the second value if they need
 * only one ID number.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/pg_shmem.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_SHMEM_H
#define PG_SHMEM_H

#include "storage/dsm_impl.h"

typedef struct PGShmemHeader    /* standard header for all Postgres shmem */
{
    int32        magic;            /* magic # to identify Postgres segments */
#define PGShmemMagic  679834894
    pid_t        creatorPID;        /* PID of creating process */
    Size        totalsize;        /* total size of segment */
    Size        freeoffset;        /* offset to first free space */
    dsm_handle    dsm_control;    /* ID of dynamic shared memory control seg */
    void       *index;            /* pointer to ShmemIndex table */
#ifndef WIN32                    /* Windows doesn't have useful inode#s */
    dev_t        device;            /* device data directory is on */
    ino_t        inode;            /* inode number of data directory */
#endif
} PGShmemHeader;

/* GUC variable */
extern int    huge_pages;

/* Possible values for huge_pages */
typedef enum
{
    HUGE_PAGES_OFF,
    HUGE_PAGES_ON,
    HUGE_PAGES_TRY
}            HugePagesType;

#ifndef WIN32
extern unsigned long UsedShmemSegID;
#else
extern HANDLE UsedShmemSegID;
#endif
extern void *UsedShmemSegAddr;

#ifdef EXEC_BACKEND
extern void PGSharedMemoryReAttach(void);
extern void PGSharedMemoryNoReAttach(void);
#endif

extern PGShmemHeader *PGSharedMemoryCreate(Size size, bool makePrivate,
                     int port, PGShmemHeader **shim);
extern bool PGSharedMemoryIsInUse(unsigned long id1, unsigned long id2);
extern void PGSharedMemoryDetach(void);

#endif                            /* PG_SHMEM_H */
